Method for the preparation of palladium(I) tri-tert-butylphosphine bromide dimer and process for its use in isomerization reactions

Abstract

The invention provides a new method for the preparation of the dimeric Pd(l) tri-tert.-butylphosphine bromide complex, characterized by the chemical formula [Pd(μ-Br)(P t Bu 3 )] 2 . The method is based on a comproportionation reaction in which a Pd(ll) compound (═PdBr 2 ) is reacted with a Pd(0) compound (═Pd(P t Bu 3 ) 2 ) in organic solvents to yield the [Pd(μ-Br)(P t Bu 3 )] 2 compound having the Pd atoms in the formal oxidation state +1. Unreacted PdBr 2 may be reused in the process. The method is straightforward and applicable for industrial scale production and provides high product yields. Further, a new process for the isomerization of allyl ethers of the general type R 1 —C(O)—O—CH(R 2 )—C(R 3 )═CH 2 employing the compound Pdμ-Br)(P t Bu 3 )] 2 as a catalyst is disclosed.

The invention claimed is: 
     
       1. A method for the preparation of the complex of formula (I) 
       
         
           
           
               
               
           
         
       
       comprising the steps of
 (a) preparing a mixture containing bis-(tris-tert.-butyl-phosphine)-palladium(0) (Pd(P t Bu 3 ) 2 ) and palladium(II)-dibromide (PdBr 2 ) in an organic solvent and 
 (b) reacting compounds PdBr 2  and Pd(P t Bu 3 ) 2  to form the complex of formula (I), also designated as [Pd(μ-Br)(P t Bu 3 )] 2 . 
 
     
     
       2. The method according to  claim 1 , wherein step (a) comprises the sub-steps:
 (a1) mixing of PdBr 2  in a first organic solvent, 
 (a2) mixing Pd(P t Bu 3 ) 2  in a second organic solvent, 
 (a3) preparing a mixture containing PdBr 2  and the first organic solvent and Pd(P t Bu 3 ) 2  and the second organic solvent. 
 
     
     
       3. The method according to  claim 1 , further comprising the step (c) of removing un-reacted PdBr 2  from the reaction mixture. 
     
     
       4. The method according to  claim 1 , further comprising the step (d) of removing the organic solvent(s) to isolate the Pd complex of formula (I). 
     
     
       5. The method according to  claim 1 , wherein the organic solvent is an aromatic hydrocarbon solvent selected from the group of benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene or mixtures thereof. 
     
     
       6. The method according to  claim 2 , wherein the first and the second organic solvent are aromatic hydrocarbon solvents selected from the group of benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene or mixtures thereof. 
     
     
       7. The method according to  claim 1 , wherein the reaction time is in the range of 0.5 to 20 hours. 
     
     
       8. The method according to  claim 1 , wherein the reaction temperature is in the range of 10 to 60° C. 
     
     
       9. The method according to  claim 3 , wherein the un-reacted PdBr 2  is separated and re-used for the preparation of the complex of the formula (I). 
     
     
       10. The method according to  claim 4 , wherein removing of the first and the second organic solvent is made by solvent evaporation at low pressure. 
     
     
       11. The method according to  claim 1 , further comprising activating the PdBr 2  prior to use. 
     
     
       12. The method according to  claim 11 , wherein step of activating the PdBr 2  further comprises treating the PdBr 2  in an organic ketone solvent selected from the group of acetone, methylethylketone or diethylketone. 
     
     
       13. The method of  claim 11 , wherein the step of activating the PdBr 2  further comprises stirring the PdBr 2  in acetone. 
     
     
       14. A process for the isomerization of allyl esters of the formula II to enol esters, 
       
         
           
           
               
               
           
         
       
       wherein
 the substituent R 1  represents a methyl, ethyl, C 3 -C 15 -alkyl, alkyl-substituted phenyl, alkoxy-substituted phenyl, halogen-substituted phenyl, or C 5 -C 10 -aryl heteroaryl group, 
 the substituents R 2  and R 3  are independently selected from hydrogen, methyl, ethyl, C 3 -C 10  alkyl or C 5 -C 10 -aryl groups, 
 
       which comprises using [Pd(μ-Br)(P t Bu 3 )] 2  as a catalyst. 
     
     
       15. The process according to  claim 14 , wherein the substituent R 1  represents a C 3 -C 15 -alkyl, phenyl, alkyl-substituted phenyl, or C 4 -C 10 -heteroaryl group, and the substituents R 2  and R 3  are independently selected from hydrogen, methyl or ethyl or C 3 -C 10 -alkyl groups. 
     
     
       16. The process according to  claim 14 , wherein the substituent R 1  represents a C 3 -C 15 -alkyl, phenyl, o-, m- or p-tolyl, furyl, pyridyl or pyrryl group, and the substituents R 2  and R 3  are independently selected from hydrogen, methyl, ethyl or C 3 -C 10 -alkyl groups. 
     
     
       17. The process according to  claim 14 , wherein the reaction time is in the range of 0.5 to 16 hours and the reaction temperature is in the range of 20 to 120° C. 
     
     
       18. The process according to  claim 14 , further comprising introducing organic solvents from the group of aromatic hydrocarbons or from the group of ethers into a reaction mixture with the catalyst. 
     
     
       19. The method of  claim 6 , wherein the first organic solvent and the second organic solvent are the same. 
     
     
       20. The method of  claim 7 , wherein the reaction time is in the range of 1 to 16 hours. 
     
     
       21. The process of  claim 17 , wherein the reaction time is in the range of 1 to 5 hours. 
     
     
       22. The process of  claim 17 , wherein the reaction temperature is in the range of 20 to 100° C. 
     
     
       23. A process for the isomerization of allyl esters of the formula II to enol esters, 
       
         
           
           
               
               
           
         
       
       wherein
 the substituent R 1  represents a methyl, ethyl, C 3 -C 15 -alkyl, phenyl, alkyl-substituted phenyl, alkoxy-substituted phenyl, halogen-substituted phenyl, or C 4 -C 10 -heteroaryl group, 
 the substituents R 2  and R 3  are independently selected from hydrogen, methyl, ethyl, C 3 -C 10  alkyl or C 5 -C 10 -aryl groups, 
 
       which comprises using [Pd(μ-Br)(P t Bu 3 )] 2  as a catalyst. 
     
     
       24. The process of  claim 14 , wherein the substituent R 1  represents a phenyl group. 
     
     
       25. The process of  claim 23 , wherein the substituent R 1  represents a phenyl group.